https://bugs.winehq.org/show_bug.cgi?id=47302
--- Comment #4 from Fabian Maurer dark.shadow4@web.de --- The program gets its decimal separator from HKEY_CURRENT_USER\Control Panel\International\sDecimal.
For some reason it works for me now. Did you already try a fresh WINEPREFIX? If that doesn't help, do you know how to reproduce the error?